Thermal sensing device for control circuits

ABSTRACT

A thermal sensor for application to the exterior of a tube or the like comprises a thermistor supported within a rectangular casing, one end of which is urged by a spring into engagement with the tube. The portion of the casing engaging the tube comprises a heat transfer member having a surface contoured to extensively engage a portion of the tube and having a pair of legs extending inwardly of the casing and straddling the thermistor which is held in a cage-like structure in the interior of the casing. A thermal conducting cement fills voids between the thermistor and the heat transfer member.

[ Jan. 29, 1974 United States Patent [191 Adams [5 THERMAL SENSINGDEVICE FOR 3,406,366 10/1968 Kontrimas et a1. 338/25 CONTROL CIRCUITS[75] Inventor:

r med .E l @PEQQFL 3 .6 Attorney, Agent, or F [rm-Watts, Hoffman, Fisher& Heinke, Co.

[57] ABSTRACT A thermal sensor for application to the exterior of a m b,m m mc .m 0 c M A C a J [73] Assignee: Ranco Incorporated,

Ohio

[22] Filed: July 17, 1972 [21] Appl. No.: 272,316

tube or the like comprises a thermistor supported within a rectangularcasing, one end of which is urged [52] us. 338/28 73/362 AR 338/22 by aSwing engagement with the tube" The [51] Int. Clmm 6 c 7/00 tion of thecasing engaging the tube comprises a heat 338/28 22 25 26 transfermember having a surface contoured to exten- [58] Field of Search.....

sively engage a portion of the tube and having a pair of legs extendinginwardly of the casing and straddling the thermistor which is held in acage-like structure in [56] References Cited UNITED STATES PATENTS theinterior of the casing. A thermal conducting cement fills voids betweenthe thermistor and the heat transfer member.

338/25 3/1964 338/28 11 Claims, 5 Drawing Figures THERMAL SENSING DEVICEFOR CONTROL CIRCUITS Background of the Invention The present inventionrelates to temperature responsive control apparatus of the typeemploying a relatively small size sensor element, such as a thermistor,for sensing the temperature of a fluid container. In utilizing controlapparatus of the type mentioned to regulate the speed of an electricmotor driven fan for cooling the condenser of a refrigerating system,for example, a problem is presented in the application of the thermistorto the condenser so as to sense temperature changes rapidly. Oneprominent solution to the problem has been to open the wall of thecondenser tubing and insert the thermistor inside the tubing and providea seal between the circuit wire and the wall of the tubing. This methodis undesirable in that it is relatively ex pensive and subjects therefrigerating system to the hazard of leaks and the attendantdisadvantages thereof.

The Present Invention The present invention provides a device forconveniently attaching a relatively small temperature sensing element inclose heat exchange relation with the exterior of tubing of arefrigerating system or the like, so that the sensing element willrespond rapidly to temperature changes of the fluid in the tubing. Thesensing device may be readily attached to the tubing without cutting thewalls or otherwise disturbing the integrity of systems comprised of thetubing and the thermistor and the lead wires therefor are well protectedand are conveniently available for connection in a control circuit.

The invention also contemplates a casing for supporting and enclosingthe thermistor which can be formed by nesting two identical casingmembers together.

Other objects and advantages of the invention will be apparent from thefollowing description of a preferred form of the invention, referencebeing made to the accompanying drawings wherein:

FIG. 1 is a front elevational view of a thermal sensing device attachedto a refrigerant condenser tube for sensing the temperature of therefrigerant in the condenser;

FIG. 2 is a side view of the sensing device shown in FIG. 1 taken alongline 22 of FIG. 1;

FIG. 3 is a fragmentary sectional view of the sensing device takensubstantially along line 3-3 of FIG. 2 and on a larger scale;

FIG. 4 is a sectional view taken substantially along line 4--4 of FIG.3; and

FIG. 5 is an exploded elevational view of disassembled components of thesensing device.

Referring to the drawings, a temperature device is shown for securing athermistor 11 in close heat transfer relation with a pipe or tubing T.The sensing device 10 may form a component of an electronic controlcircuit for controlling the speed of a fan for circulating air over thecondenser, for example. The control circuit is not shown as it is notessential to the understanding of this invention.

The sensing device 10 comprises a casing 12, one end 13 of which isconcave and receives a heat transfer member 14. The member 14 has asemicylindrical portion 15 which is adapted to engage the exterior ofthe tubing T, and the inside diameter of the semicylindrical portioncorresponds to the outside diameter of the tube so that a substantialarea of the member 14 may be maintained in contact with the outside wallof the tubing. The sensing device 10 is secured to the tubing T with themember 14 in contact with the tubing, as just described, by a springclip 16. The clip 16 comprises a spring wire having hooked ends whichengage in recesses 17 at opposite sides of the lower end of the casing12, as viewed in FIG. 3. The intermediate portion of the clip overliesthe tubing T and a coil 18 formed by the wire maintains a tension whichurges the casing 12 to the tubing.

The casing 12 is comprised of two identical open box-like molded members20,21 which are secured in nesting relationship by rivets 22, 23. Forsake of clarity, the parts of the casing member 21 which correspond tolike parts of the casing 20 are designated by the same referencecharacters having a prime added thereto. Referring more specifically tocasing member 20 as shown in FIGS. 3, 4 and 5, the member comprises agenerally rectangular side panel 24 having the semicylindrical recess 13at the upper end. Two side walls 25,26 are formed integral with thepanel 24 and extend from the bottom edge 27 upwardly, as viewed in thedrawings. A portion 30 of the wall 25 angles inwardly as does theportion 31 of wall 26. The wall portion 30 turns upwardly and extends tothe edge 13. The upper end of wall portion 31 terminates short of theedge 13. The section of the wall 26 which extends parallel to the sideedges of the panel 24 is inset from the adjacent edge of the panel thedistance of the thickness of the side wall 25 except at the lower endportion 32 which is offset flush with the edge of the panel. The sectionof the wall 25 which extends parallel to the side of the panel 24 isflush with the adjacent edge of the panel 24. The lower end portion ofthe wall 25 is offset the width of wall 26 as seen at 33. A shallowupper side wall 34 forms a continuation of the wall 25 from the angledportion 30 and terminates at the upper edge of the panel 24. A secondshallow wall section 35 on the side of the panel 24 opposite the wall 34extends from the upper edge of the panel and terminates short of theturned-in portion 31 of wall 26. The wall 34 is flush with the adjacentside edge of the panel.

A semicylindrical wall 36 extends inwardly from the panel 24 andpartially surrounds a hole 37 through the panel for receiving the rivet22. A second semicylindrical wall section 40 extends from the panel 24opposite the wall 36. The inside of the semicylindrical portion of wall40 is spaced from the hole 37 the thickness of the wall 36. One side 41of the wall 40 is straight and is parallel to the inside of the wallportion 31. The upper end of the side 41 terminates to form a shoulder42.

A narrow wall or flange 43 projects from the panel 24 and is spaced fromthe wall part 30 to form a channel 44 of the same width as the thicknessof the wall part 31. A bridge member 45 is formed between the upper endof the wall 43 and the shoulder 42. The dimension of the bridge member45 from the surface of panel 24 outwardly from the panel is somewhatless than one-half the similar dimension of the shoulder 42.

A lug 46 is formed on the center line of the panel 24 and has its upperedge flush with the edge 13 of the panel. Two short diverging ribs 47,48extend on either side of the lug.

The panel 24 has a longitudinally extending central rib 50. The lowerportion of the rib 50 is widened and has an opening 51 therethroughthrough which the rivet 23 extends. Transversely extending ribs 52, 53,

54, 55 lend reinforcement to the panel 24. The rib 52 extends from theside wall 26 and terminates short of the rib 50. A notch 56 in the rib52 forms a guide for a lead wire of the thermistor 11 describedhereinafter. The rib 53 extends laterally from rib 50 and terminatesshort of the side wall 25 to accommodate a second lead wire ofthermistor 11. The lower end of the wall 43 has an enlargement having anotch 58 which forms a second guide for a thermistor lead wire.

The thermistor 11 is of conventional form, comprising a disc shaped bodyhaving terminal wires 60,61 attached to opposite faces. The ends of thewires 60,61 are soldered to insulated lead wires 64,65, respectively.

When the sensing device is to be assembled, the thermistor 11 is firstplaced in the casing between the shoulders 45 and 46 and disposed withits circular surfaces facing opposite sides of the casing member. Thewire 60 is laid in the channel 44 and is lodged in the notch 58. Thelead wire 64 lies across the rib 53 and the insulated portion of thewire 60 extends from the bottom of the casing member and lies betweenthe side wall and the enlarged portion of the rib 50. The wire 61 islaid in the channel formed by the wall sections 31 and 41 and is lodgedin the notch 56. The insulated portion of wire 65 extends from the lowerend of the casing member and lies between the side wall 26 and the lowerenlarged end of the rib 50. The open side of cover member 21 is thenbrought face to face with the cover member 20 with the edges of theholes 37,37 and 51,51 in alignment. The casing members are then movedinto nesting relationship so that the side wall 25 will lie alongsidethe outer side of the side wall 26 with its outer edge approximatelyabutting the outer edge portion of the panel 24'. The side wall 25 ofeasing member 21 then lies alongside the side wall 26 and its outer edgelies along the outer edge of the panel 24. The portions 31' and 32' ofthe wall 26 nest with the portions 30,33 of the wall 25. Likewise, theportions 31,32 of the wall 26 nest with the portions ,33' of the wall25'. The confronting edges of the pairs of flanges 34,35 and 34,35 arespaced and form slots to receive the spring 16 when it is applied to thecasing when the sensing device is installed on a condenser.

The semicylindrical wall 36 nests inside the semicylindrical wall 40'and the semicylindrical wall 36 nests inside the semicylindrical wall40. These semicylindrical walls cooperate to form bushings through whichthe rivets 22,23 are inserted and crimped to secure the two casingmembers together. The bridge members 42,42, the lugs 46,46, the ribs47,47, 48,48 cooperate to form a cage for capturing the thermistor 11.

When the casing members 20,21 are secured together, the wire 60 will beheld in notch 56' of the rib 52. The uninsulated portion of wire 64 willoverlie the rib 53 and the uninsulated portion of the wire 65 willunderlie the rib 53 as viewed in FIG. 3.

The wires 64,65 may have terminals, not shown, for connection in the fancontrol circuit.

After the casing is assmebled as described, the heat transfer member 14is inserted into the upper end of the casing. The heat transfer member14 has a pair of legs 70,71 which project from the convex side thereofand are formed to be received between the wall portions 32,32 and theribs 47,48 and 47',48'. A body of suitable heat conducting cement 72 isdisposed between the circular faces of the thermistor Ill and theadjacent leg of the member 14. Preferably, the cement in a viscous formis conveniently injected onto opposite faces of the thermistor and themember 14 is positioned in nesting relation in the received portion 13,as shown. The legs, 70, 71 displace a portion of the cement, which flowsabout the thermistor and into the voids of the structure forming thecage about the thermistor. The cement also adheres to the surfaces ofthe legs 70,71. Preferably, the cement is an epoxy with aluminum powderfiller. The cement is then cured and solidifies to secure the thermistorin place and provide a good heat transfer body between the legs of themember 14 and the thermistor.

It will be seen that when the assembled casing 21 is applied to the tubeT as shown and described, a rapid heat transfer is effected between thewalls of the tube and the transistor. The casing provides a convenienthandling agency for the transistor as well as mechanical and electricalshielding thereof.

1 claim:

1. A temperature sensing device comprisigng a casing having an openingin one end, said casing comprising two similar open box-like casingmembers and means securing said casing members together with the opensides thereof facing toward the other casing member, a heat conductingmember disposed in said opening and comprising a portion having asubstantial surface exposed at said one end of said casing and havingspaced projections extending into said casing, a temperature sensitiveelement in said casing adjacent said opening, each casing member havingprojections from a wall thereof forming shoulders, said shoulderscooperating to retain said element in said casing, and means in saidcasing for positioning said element between two of said projections onsaid heat conducting member.

2. A temperature sensing device as defined in Claim 1 furthercharacterized by a body of heat conducting cement interconnecting saidelement and said projections on said heat conducting member.

3. A temperature sensing device comprising a casing comprising agenerally rectangular body having a concave end portion defining anopening, a heat conduct ing member disposed in said opening andcomprising a semicylindrical portion nested in said concave end portionof said casing and having a substantial surface exposed at said casingend portion, said heat conducting member comprising spaced projectionsextending into said casing, a temperature sensitive element in saidcasing adjacent said opening, means in said casing for positioning saidelement between two of said projections on said member, and spring meansengaging said casing and adapted to urge said casing in a direction tomaintain said heat conducting member in engagement with an object atsaid casing end portion.

4. A temperature sensing device comprising a casing having an opening inone end, a heat conducting member disposed in said opening andcomprising a portion having a substantial surface exposed at said oneend of said casing'and having spaced projections extending into saidcasing, a disc-shaped temperature sensitive element in said casingadjacent said opening, means in said casing for positioning said elementbetween two of said projections on said member, said element havingterminal wires extending from opposite faces, and said casing comprisingwall members forming guide channels for said terminal wires,respectively.

5. In a device for sensing the temperature of an ject:

a. a support casing;

b. a temperature sensitive element disposed in said casing and definingat least two major surfaces;

c. a heat conducting member supported by said casing and comprising:

i. a first heat transfer face extending along an external side of saidcasing and configured to provide for heat transfer relationship with theobject;

ii. at least second and third heat transfer faces extending into saidcasing and closely adjacent respective ones of said major surfaces ofsaid temperature sensitive element to provide for heat transfer betweensaid second and third heat transfer faces and said respective majorsurfaces;

iii. said heat conducting member constructed to provide for relativelylow impedance conductive heat flow between said first heat transfer faceand said second and third heat transfer faces; and,

d7 support means for supporting said casing with said first heattransfer face in heat exchange relationship with the object.

6. The device as claimed in claim 5 wherein said heat sensitive elementis electrically conductive and has electrical properties which change inresponse to changes in temperature of said element and furthercomprising insulating means for electrically insulating said majorsurfaces from said second and third heat transfer faces withoutsubstantially impeding heat transfer therebetween.

7. The device claimed in claim 5 wherein said at least two majorsurfaces of said temperature sensitive member and said second and thirdheat transfer faces extend in directions generally transverse to saidfirst heat transfer face of said heat conductive member.

8. The device claimed in claim 7 wherein said temperature sensitiveelement is generally disc-shaped and said heat conducting memberincludes projecting portions on which said second and third heattransfer faces are defined.

9. The device claimed in claim 8 wherein said heat sensitive element isformed at least in part by material having an electrical impedance whichvaries in accordance with changes in the temperature of the material andfurther comprising electrical conductors electrically connected to saidelement and extending from said casing and heat conducting electricalinsulating means interposed between said element and conductors and saidheat conducting member.

10. The device claimed in claim 9 wherein said first heat tranfer faceincludes at least a portion which is shaped to conform to a portion ofthe object and said support means comprises a resilient member reactingbetween said device and the object to resiliently maintain said firstheat transfer face portion in heat conducting contact with the surfaceportion of the object.

11. The device claimed in claim 5 wherein said first heat transfer faceincludes at least a portion which is shaped to conform to a portion ofthe object and said support means comprises a resilient member reactingbetween said device and the object to resiliently maintain said firstheat transfer face portion in heat conducting contact with the surfaceportion of the object. =l=

1. A temperature sensing device comprisigng a casing having an openingin one end, said casing comprising two similar open boxlike casingmembers and means securing said casing members together with the opensides thereof facing toward the other casing member, a heat conductingmember disposed in said opening and comprising a portion having asubstantial surface exposed at said one end of said casing and havingspaced projections extending into said casing, a temperature sensitiveelement in said casing adjacent said opening, each casing member havingprojections from a wall thereof forming shoulders, said shoulderscooperating to retain said element in said casing, and means in saidcasing for positioning said element between two of said projections onsaid heat conducting member.
 2. A temperature sensing device as definedin Claim 1 further characterized by a body of heat conducting cementinterconnecting said element and said projections on said heatconducting member.
 3. A temperature sensing device comprising a casingcomprising a generally rectangular body having a concave end portiondefining an opening, a heat conducting member disposed in said openingand comprising a semicylindrical portion nested in said concave endportion of said casing and having a substantial surface exposed at saidcasing end portion, said heat conducting member comprising spacedprojections extending into said casing, a temperature sensitive elementin said casing adjacent said opening, means in said casing forpositioning said element between two of said projections on said member,and spring means engaging said casing and adapted to urge said casing ina direction to maintain said heat conducting member in engagement withan object at said casing end portion.
 4. A temperature sensing devicecomprising a casing having an opening in one end, a heat conductingmember disposed in said opening and comprising a portion having asubstantial surface exposed at said one end of said casing and havingspaced projections extending into said casing, a disc-shaped temperaturesensitive element in said casing adjacent said opening, means in saidcasing for positioning said element between two of said projections onsaid member, said element having terminal wires extending from oppositefaces, and said casing comprising wall members forming guide channelsfor said terminal wires, respectively.
 5. In a device for sensing thetemperature of an object: a. a support casing; b. a temperaturesensitive element disposed in said casing and defining at least twomajor surfaces; c. a heat conducting member supported by said casing andcomprising: i. a first heat transfer face extending along an externalside of said casing and configured to provide for heat transferrelationship with the object; ii. at least second and third heattransfer faces extending into said casing and closely adjacentrespective ones of said major surfaces of said temperature sensitiveelement to provide for heat transfer between said second and third heattransfer faces and said respective major surfaces; iii. said heatconducting member constructed to provide for relatively low impedanceconductive heat flow between said first heat transfer face and saidsecond and third heat transfer faces; and, d. support means forsupporting said casing with said firsT heat transfer face in heatexchange relationship with the object.
 6. The device as claimed in claim5 wherein said heat sensitive element is electrically conductive and haselectrical properties which change in response to changes in temperatureof said element and further comprising insulating means for electricallyinsulating said major surfaces from said second and third heat transferfaces without substantially impeding heat transfer therebetween.
 7. Thedevice claimed in claim 5 wherein said at least two major surfaces ofsaid temperature sensitive member and said second and third heattransfer faces extend in directions generally transverse to said firstheat transfer face of said heat conductive member.
 8. The device claimedin claim 7 wherein said temperature sensitive element is generallydisc-shaped and said heat conducting member includes projecting portionson which said second and third heat transfer faces are defined.
 9. Thedevice claimed in claim 8 wherein said heat sensitive element is formedat least in part by material having an electrical impedance which variesin accordance with changes in the temperature of the material andfurther comprising electrical conductors electrically connected to saidelement and extending from said casing and heat conducting electricalinsulating means interposed between said element and conductors and saidheat conducting member.
 10. The device claimed in claim 9 wherein saidfirst heat tranfer face includes at least a portion which is shaped toconform to a portion of the object and said support means comprises aresilient member reacting between said device and the object toresiliently maintain said first heat transfer face portion in heatconducting contact with the surface portion of the object.
 11. Thedevice claimed in claim 5 wherein said first heat transfer face includesat least a portion which is shaped to conform to a portion of the objectand said support means comprises a resilient member reacting betweensaid device and the object to resiliently maintain said first heattransfer face portion in heat conducting contact with the surfaceportion of the object.